Time division multiplexed limited switch dynamic logic

ABSTRACT

A method for increasing performance in a limited switch dynamic logic (LSDL) circuit includes precharging a dynamic node during a precharge phase of a first and second evaluation clock signal. The dynamic node is evaluated to a first logic value in response to one or more first input signals of a first evaluation tree during an evaluation phase of the first evaluation clock signal. The dynamic node is evaluated to a second logic value in response one or more second input signals of a second evaluation tree during an evaluation phase of the second evaluation clock signal. A signal of the LSDL circuit is outputted in response to the dynamic node according to an output latch clock signal.

RELATED APPLICATION INFORMATION

This application is a Continuation application of allowed co-pendingU.S. patent application Ser. No. 13/524,562 filed on Jun. 15, 2012,which is itself a Continuation of issued U.S. Pat. No. 8,493,093, filedJun. 12, 2012, both of which are incorporated herein by reference intheir entirety.

BACKGROUND

1. Technical Field

The present invention relates to limited switch dynamic logic circuits,and more particularly to high-speed time division multiplexed limitedswitch dynamic logic circuits to enable high-speed double pumping.

2. Description of the Related Art

Whether by frequency scaling or parallelism, as microprocessorperformance increases, the demand for high-speed memory growsdramatically. To sustain system performance trends, increasing memorycapacity requirements is critical. However, memory capacity is generallya tradeoff with memory performance. Double pumping may be able tosatisfy these tradeoff requirements, particularly with a multi-portregister file (RF) or content addressable memory (CAM). Double pumpingtransfers data on both the rising and falling edge of the clock signal.By using both edges of the clock, the data signals operate with the samelimiting frequency, thereby doubling the data transmission rate. Inorder to apply double pumping, a high-speed time division multiplexingcircuit is needed.

SUMMARY

A limited switch dynamic logic (LSDL) circuit includes a dynamic logiccircuit and a static logic circuit. The dynamic logic circuit includes aprecharge device configured to precharge a dynamic node during aprecharge phase of a first evaluation clock signal and a secondevaluation clock signal. A first evaluation tree is configured toevaluate the dynamic node to a first logic value in response to one ormore first input signals during an evaluation phase of the firstevaluation clock signal. A second evaluation tree is configured toevaluate the dynamic node to a second logic value in response to one ormore second input signals during an evaluation phase of the secondevaluation clock signal. A static logic circuit is configured to providean output of the LSDL circuit in response to the dynamic node accordingto an output latch clock signal.

A limited switch dynamic logic (LSDL) circuit includes a dynamic logiccircuit and a static logic circuit. The dynamic logic circuit includes aprecharge device configured to precharge a dynamic node during aprecharge phase of a first evaluation clock signal and a secondevaluation clock signal. A first evaluation tree is configured toevaluate the dynamic node to a first logic value in response to one ormore first input signals during an evaluation phase of the firstevaluation clock signal. A first foot device is coupled between anoutput of the first evaluation tree and the dynamic node to controlevaluation of the dynamic node by the first evaluation tree according tothe first evaluation clock signal. A second evaluation tree isconfigured to evaluate the dynamic node to a second logic value inresponse to one or more second input signals during an evaluation phaseof the second evaluation clock signal. A second foot device is coupledbetween an output of the second evaluation tree and the dynamic node tocontrol evaluation of the dynamic node by the second evaluation treeaccording to the second evaluation clock signal. A static latch circuitis configured to provide an output of the LSDL circuit in response tothe dynamic node according to an output latch clock signal, wherein theoutput latch clock signal is a logical OR of the first and secondevaluation clock signals.

A limited switch dynamic logic (LSDL) circuit includes a dynamic logiccircuit and a static logic circuit. The dynamic logic circuit includes afirst precharge device configured to precharge a first dynamic nodeduring a precharge phase of a first evaluation clock signal. A firstevaluation tree is configured to evaluate the first dynamic node to afirst logic value in response to one or more first input signals duringan evaluation phase of the first evaluation clock signal. A secondprecharge device is configured to precharge a second dynamic node to asecond logic value during a precharge phase of a second evaluation clocksignal. A second evaluation tree is configured to evaluate the seconddynamic node in response to one or more second input signals during anevaluation phase of the second evaluation clock signal. A static logiccircuit is configured to provide an output of the LSDL circuit inresponse to at least one of the first dynamic node during the evaluationphase of the first evaluation clock signal and the second dynamic nodeduring the evaluation phase of the second evaluation clock signal.

A method to increase performance in a limited switch dynamic logic(LSDL) circuit includes precharging a dynamic node during a prechargephase of a first and second evaluation clock signal. The dynamic node isevaluated to a first logic value in response to one or more first inputsignals of a first evaluation tree during an evaluation phase of thefirst evaluation clock signal. The dynamic node is evaluated to a secondlogic value in response one or more second input signals of a secondevaluation tree during an evaluation phase of the second evaluationclock signal. A signal of the LSDL circuit is outputted in response tothe dynamic node according to an output latch clock signal.

A method to increase performance in a limited switch dynamic logic(LSDL) circuit includes precharging a dynamic node during a prechargephase of a first and second evaluation clock signal. The dynamic node isevaluated to a first logic value in response to one or more first inputsignals of the first evaluation tree during an evaluation phase of thefirst evaluation clock signal. Evaluation of the dynamic node by thefirst evaluation tree is controlled according to the first evaluationclock signal. The dynamic node is evaluated to a second logic value inresponse to one or more second input signals of the second evaluationtree during an evaluation phase of the second evaluation clock signal.Evaluation of the dynamic node by the second evaluation tree iscontrolled according to the second evaluation clock signal. A signal ofthe LSDL circuit is outputted in response to the dynamic node accordingto an output latch clock signal, wherein the output latch clock signalis a logical OR of the first and second evaluation clock signals.

A method to increase performance in a limited switch dynamic logic(LSDL) circuit includes precharging a first dynamic node during aprecharge phase of a first evaluation clock signal. The first dynamicnode is evaluated to a first logic value in response to one or morefirst input signals of a first evaluation tree during an evaluationphase of the first evaluation clock signal. A second dynamic node isprecharged during a precharge phase of a second evaluation clock signal.The second dynamic node is evaluated to a second logic value in responseto one or more second input signals of a second evaluation tree duringan evaluation phase of the second evaluation clock signal. A signal ofthe LSDL circuit is outputted in response to at least one of the firstdynamic node during the evaluation phase of the first evaluation clocksignal and the second dynamic node during the evaluation phase of thesecond evaluation clock signal.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 shows a block/flow diagram, in partial schematic form, of a priorart LSDL device combining a dynamic circuit front end with a simplelatch;

FIG. 2 shows a block/flow diagram, in partial schematic form, of an LSDLdevice in NAND form including two evaluation trees tied to two separateclocks to enable double pumping, in accordance with one illustrativeembodiment;

FIG. 3 shows a timing diagram for first and second clocks for an LSDLdevice in NAND form in a double pumping implementation, in accordancewith one illustrative embodiment;

FIG. 4 shows a block/flow diagram, in partial schematic form, of an LSDLdevice to enable double pumping with a simplified circuit architectureachieved by implementing a third clock signal, in accordance with oneillustrative embodiment;

FIG. 5 shows a timing diagram for first, second and third clocks for anLSDL device in a double pumping implementation with a simplified circuitarchitecture, in accordance with one illustrative embodiment;

FIG. 6 shows a block/flow diagram of a system/method for enabling doublepumping in an LSDL device in NAND form using two evaluation trees tiedto two separate clocks, in accordance with one illustrative embodiment;and

FIG. 7 shows a block/flow diagram of a system/method for enabling doublepumping in an LSDL device with a simplified circuit architecture, inaccordance with one illustrative embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present principles, time division multiplexed(TDM) limited switch dynamic logic (LSDL) circuits and methods areprovided. LSDL circuits are a combination of dynamic logic circuits andstatic logic circuits.

In one embodiment, an LSDL circuit in NAND form is configured to enabledouble pumping by performing logic evaluation operations in both halvesof a processor clock cycle. An LSDL circuit in NAND form may includefirst and second evaluation clock signals. Initially, the first andsecond evaluation clock signals are simultaneously low, causing a firstprecharge device to precharge a first dynamic node to a logic high valueand a second precharge device to precharge a second dynamic node to alogic high value. During a first evaluation phase, e.g., in a first halfof a clock cycle, the first evaluation clock signal pulses high, causinga first evaluation tree to evaluate the first dynamic node to a logichigh or logic low value according to one or more first input signals ofthe first evaluation tree. A static latch provides an output of the LSDLcircuit in NAND form in response to the value of the first dynamic nodeduring an evaluation phase of the first evaluation clock. The firstevaluation clock signal then returns low to a precharge phase. During asecond evaluation phase, e.g., in a second half of a clock cycle, thesecond evaluation clock signal pulses high, causing a second evaluationtree to evaluate the second dynamic node to a logic high or logic lowvalue according to one or more second input signals of the secondevaluation tree. The static latch provides an output of the LSDL circuitin NAND form in response to the value of the second dynamic node duringan evaluation phase of the second evaluation clock. The second clocksignal then returns low to a precharge phase. Advantageously, thepresent principles provide an LSDL device in NAND form to enablehigh-speed double pumping such that logic evaluation operations areperformed in each half of a clock cycle to increase performance.

In another embodiment, an LSDL circuit may include a first evaluationclock signal, a second evaluation clock signal, and an output latchclock signal. Preferably, the output latch clock signal is generated bythe logical OR of the first evaluation clock signal and the secondevaluation clock signal. Initially, the first and second evaluationclock signals and the output latch clock signal are simultaneously low,causing a precharge device to precharge the dynamic node to a logic highvalue. During a first evaluation phase, e.g., in a first half of a clockcycle, the first evaluation clock signal and the output latch clocksignal pulse high, causing a first evaluation tree to evaluate thedynamic node to a logic high or logic low value according to one or morefirst input signals. A static latch provides an output of the LSDLcircuit in response to the value on the dynamic node according to theoutput latch clock signal. The first clock signal and the output latchclock signal then return low to a precharge phase. During a secondevaluation phase, e.g., in a second half of a clock cycle, the secondclock and the output latch clock signal pulse high, causing a secondevaluation tree to evaluate the dynamic node to a logic high or logiclow value according to one or more second input signals. The staticlatch provides an output of the LSDL circuit in response to the value onthe dynamic node according to the output latch clock signal. The secondevaluation clock signal and the output latch clock signal then returnlow to a precharge phase. Advantageously, the present principles providean LSDL device with a simplified circuit architecture that enablesdouble pumping. The reduced number of devices will lead to an increasein performance. In addition, by implementing double-pumping in an LSDLdevice, logic evaluation operations are performed in each half of aclock cycle to further increase performance.

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods and apparatus(systems) according to embodiments of the invention. The flowchart andblock diagrams in the Figures illustrate the architecture,functionality, and operation of possible implementations of systems andmethods according to various embodiments of the present invention. Itshould be noted that, in some alternative implementations, the functionsnoted in the block may occur out of the order noted in the figures. Forexample, two blocks shown in succession may, in fact, be executedsubstantially concurrently, or the blocks may sometimes be executed inthe reverse order, depending upon the functionality involved.

It is to be understood that the present invention will be described interms of given illustrative circuit architectures; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention. It willalso be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

A design for an integrated circuit chip may be created in a graphicalcomputer programming language, and stored in a computer storage medium(such as a disk, tape, physical hard drive, or virtual hard drive suchas in a storage access network). If the designer does not fabricatechips or the photolithographic masks used to fabricate chips, thedesigner may transmit the resulting design by physical means (e.g., byproviding a copy of the storage medium storing the design) orelectronically (e.g., through the Internet) to such entities, directlyor indirectly. The stored design is then converted into the appropriateformat (e.g., GDSII) for the fabrication of photolithographic masks,which typically include multiple copies of the chip design in questionthat are to be formed on a wafer. The photolithographic masks areutilized to define areas of the wafer (and/or the layers thereon) to beetched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a block/flow diagram, inpartial schematic form, illustratively depicts a prior art limitedswitch dynamic logic (LSDL) device 100. LSDL is a combination of staticlogic circuits and dynamic logic circuits.

LSDL device 100 receives a plurality, n, of inputs 102 provided toevaluation tree 104. Evaluation tree 104 performs Boolean computationson inputs 102 to provide an output on the dynamic node 110 (during anevaluation phase). Evaluation tree 104 is coupled between the drain ofprecharge device p-channel field effect transistor (PFET) 106 and thedrain of foot device n-channel field effect transistor (NFET) 108. Thejunction of the evaluation tree 104 and the drain of PFET 106 form thedynamic node 110. PFET 106 and NFET 108 are clocked by clock signal 120.When clock signal 120 is low (i.e., the precharge phase), PFET 106 isturned on to precharge dynamic node 110 to a logic high value. Whenclock signal 120 is high (i.e., the evaluation phase), PFET 106 isturned off and NFET 108 is turned on, allowing dynamic node 110 to beselectively discharged to ground according to the Boolean combination ofinputs 102 from evaluation tree 104.

Dynamic node 110 is coupled to the common junction of the gates ofpre-driver devices PFET 112 and NFET 114. PFET 112 and NFET 114 form aninverter pair to invert the signal on the dynamic node 110 and providegain. PFET 112 and NFET 114 are serially coupled to parallel NFETs 116and 118. Header device NFET 116 is clocked by clock signal 120. Feedbackdevices NFET 118 and PFET 122 receive feedback from the output 130 ofLSDL device 100 and are used to restore charge to the latched value.NFET 118 and PFET 122 allow the value in the latch to be held as long asthe clock is kept low (i.e., precharge phase). A latch is formed byinverter pair PFET 112 and NFET 114 and feedback devices NFET 118 andPFET 122. LSDL device 100 may include cut feedback device PFET 124,which is clocked by clock signal 120. PFET 124 cuts the feedback throughPFET 122 during the evaluation phase to prevent conflict betweenfeedback devices PFET 122 and NFET 114 when node 126 switches from logichigh to logic low. The signal at node 126 drives the output 130 byoutput driver inverter 128.

Referring now to FIG. 2, a block/flow diagram, in partial schematicform, illustratively depicts a time division multiplexed LSDL device inNAND form 200 to enable double pumping, in accordance with oneembodiment. NAND form LSDL device 200 receives a plurality, n, oflogical inputs 202 provided to evaluation tree 204 (e.g., NFETevaluation tree). Evaluation tree 204 performs Boolean logiccomputations on inputs 202 to provide a logical output on a firstdynamic node 214 during an evaluation phase. NAND form LSDL device 200also receives a plurality, m, of inputs 206 into evaluation tree 208(e.g., NFET evaluation tree). The number of inputs 202 and 206 do notnecessarily have to be equal. Evaluation tree 208 performs Booleancomputations on inputs 206 to provide an output on a second dynamic node222 during an evaluation phase.

Evaluation tree 204 is coupled between the drain of precharge devicePFET 210 and the drain of foot device NFET 212. The junction of theevaluation tree 204 and PFET 210 forms the first dynamic node 214. PFET210 and NFET 212 are clocked with a (e.g., early phase) first evaluationclock signal 216. When the first evaluation clock signal 216 is low,during the precharge phase, PFET 210 is turned on to charge dynamic node214 to a logic high value and NFET 212 is turned off to prevent thestatic latch circuit from burning dynamic power. During the prechargephase, NFET 212 prevents dynamic node 214 from being evaluated byevaluation tree 204, regardless of input 202. When the first evaluationclock signal 216 is high, during the evaluation phase, PFET 210 isturned off and NFET 212 is turned on, allowing dynamic node 214 to beselectively discharged to ground according to the Boolean combination ofinputs 202 from evaluation tree 204. In one embodiment, PFET 210 may besized to be the smallest device capable of precharging the dynamic node214 within the allocated precharge time.

Evaluation tree 208 is coupled between the drain of precharge devicePFET 218 and the drain of foot device NFET 220. The junction of theevaluation tree 208 and PFET 218 forms a second dynamic node 222. PFET218 and NFET 220 are clocked with a (e.g., late phase) second evaluationclock signal 224. Advantageously, by utilizing two clocks, performancemay be doubled. When the second evaluation clock signal 224 is low,during the precharge phase, PFET 218 is turned on to charge dynamic node222 to a logic high value and NFET 220 is turned off to prevent thestatic latch circuit from burning dynamic power. During the prechargephase, NFET 218 prevents dynamic node 222 from being evaluated byevaluation tree 208, regardless of inputs 206. When the secondevaluation clock signal 224 is high, during the evaluation phase, PFET218 is turned off and NFET 220 is turned on, allowing dynamic node 222to be selectively discharged to ground according to the Booleancombination of inputs 206 from evaluation tree 208. In one embodiment,PFET 218 may be sized to be the smallest device capable of prechargingthe dynamic node 222 within the allocated precharge time.

In a preferred embodiment, first and second evaluation clock signals 216and 224 are configured in a double-pumping implementation; however, itis noted that the present principles are much broader, as otherconfigurations of clock signals 216 and 224 are also contemplated.Referring for a moment to FIG. 3, with continued reference to FIG. 2, atiming diagram 300 is illustratively depicted for the first evaluationclock signal 216, the second evaluation clock signal 224 and a centralprocessing unit (CPU) clock 302 configured in a double-pumpingimplementation, in accordance with one embodiment. Initially, just priorto time T1 304, first and second evaluation clock signals 216 and 224are simultaneously low (i.e., precharge phase), allowing prechargedevices 210 and 218 to precharge dynamic nodes 214 and 222,respectively. In a first half of a cycle of CPU clock 302, such asbetween times T1 304 and T2 306 (e.g., at rising edge 314), the firstevaluation clock signal 216 pulses high 316, allowing evaluation tree204 to evaluate dynamic node 214 according to inputs 202. An output 250of LSDL device in NAND form 200 is determined in response to dynamicnode 214 and the first evaluation clock signal 216 then returns low to aprecharge phase. In a second half of a cycle of CPU clock 302, such asbetween times T2 306 and T3 308 (e.g., at the falling edge 318), thesecond evaluation clock signal 224 pulses high 320, allowing evaluationtree 208 to evaluate dynamic node 222 according to inputs 206. Theoutput 250 is determined in response to dynamic node 222 and then clocksignal 224 returns low to a precharge phase. This process continues overtimes T3 308, T4 310, T5 312, etc. Advantageously, by implementing adouble-pumping configuration, a logic evaluation operation is performedin each half of a cycle of CPU clock 302.

Referring back to FIG. 2, first dynamic node 214 is coupled to thecommon junction of the gates of pre-driver devices PFET 226 and NFET228. Second dynamic node 222 is coupled to the common junction of thegates of pre-driver devices PFET 230 and NFET 232. Pre-driver devicesPFETs 226 and 230 and NFETs 228 and 232 form a NAND gate. When dynamicnodes 214 and 222 are high, NFETs 228 and 232 will conduct, PFETs 226and 230 will not conduct, resulting in a conductive path between outputnode 246 and ground, bringing the output node 246 low. When either ofdynamic nodes 214 and 222 are low, one of NFETs 228 and 232 will notconduct, one of PFETs 226 and 230 will conduct, resulting in aconductive path between output node 246 and the voltage source, bringingthe output node 246 high. It is noted that while PFETs 226 and 230 andNFETs 228 and 232 perform a logical NAND function, other logicalfunctions are contemplated within the scope of the present invention.

In one embodiment, parallel foot devices NFETs 234 and 236 are seriallycoupled to the NAND gate. NFETS 234 and 236 prevent the forwardpropagation of the signal on dynamic nodes 214 and 222 during theprecharge phase. In one embodiment, where evaluation trees 204 and 208are guaranteed to be off when the dynamic front end is in the prechargephase, foot devices 212 and 220 are not necessary. NFET 234 is clockedby the first evaluation clock signal 216 and prevents the forwardpropagation of the signal on dynamic node 214 during the precharge phaseof clock signal 216. NFET 236 is clocked by the second evaluation clocksignal 224 and prevents the forward propagation of the signal on dynamicnode 222 during the precharge phase of clock signal 224.

Feedback devices PFET 238 and NFET 240 receive feedback from the output250 of the LSDL device in NAND form 200 to restore the charge to thelatched value. PFET 238 and NFET 240 allow the value in the latch to beheld as long as the clocks 216 and 224 are kept low (i.e., duringprecharge phase). A latch is formed by PFET 238 and NFET 240. In oneembodiment, LSDL device in NAND form 200 may include cut feedbackdevices, PFETs 242 and 244, which are clocked by the second and firstevaluation clock signals 224 and 216, respectively. PFETs 242 and 244cut the feedback through PFET 238 during the evaluation phase to preventconflict between PFET 238 and NFETs 234 and 236 when node 246 switchesfrom logic high to logic low. PFETs 242 and 244 increase loading ontheir respective clock signals, which leads to an increase in clockpower consumption, but provides increased speed and circuit robustness.The signal at node 246 drives the output 250 by the output driverinverter 248 to mitigate noise propagation from dynamic nodes 214 and222.

Advantageously, the time division multiplexed LSDL device in NAND form200 is configured to implement double-pumping. As such, a logicevaluation operation is performed in each half of a clock cycle. Byutilizing two clock signals (clock signals 216 and 224), performance maybe doubled.

Referring now to FIG. 4, a block/flow diagram, in partial schematicform, illustratively depicts an LSDL device 400 to enable double pumpingwith a simplified circuit architecture, in accordance with oneembodiment. LSDL device 400 receives a plurality, n, of logical inputs402 provided to NFET evaluation tree 404. Evaluation tree 404 performsBoolean logic computations on inputs 402 to provide a logical output tothe source of foot device NFET 410. NFET 410 is clocked by a firstevaluation clock signal 414 and limits dynamic node diffusioncapacitance to evaluation tree 404 during a precharge phase of the clocksignal 414. LSDL device 400 also receives a plurality, m, of inputs 406provided to NFET evaluation tree 408. Inputs n and m do not necessarilyhave to be equal. Evaluation tree 408 performs Boolean computations oninputs 406 to provide an output to the source of foot device NFET 412.NFET 412 is switched with a second evaluation clock signal 416 andlimits dynamic node diffusion capacitance to evaluation tree 408 duringa precharge phase of the clock signal 416.

During the precharge phase, if at least one of inputs 402 and 406 arehigh, then the latched data might flip and the dynamic node 418 may bepulled down halfway. Thus, NFETs 410 and 412 are turned off during theprecharge phase to prevent dynamic node 418 from being evaluated byevaluation trees 404 and 408, regardless of inputs 402 and 406. Thejunction of the drains of NFETs 410 and 412 form the dynamic node 418.By moving foot devices NFETs 410 and 412 above evaluation trees 404 and408, diffusion capacitance from dynamic node 418 to evaluation trees 404and 408 is reduced, thereby increasing performance. In addition, sinceclocked NFETS 410 and 412 are located above the evaluation trees, theyare located closer to the output 440 of the LSDL device 400 (comparedwith NFETS 212 and 220 of LSDL device in NAND form 200 of FIG. 2) tofurther increase performance.

Dynamic node 418 is coupled to the drain of precharge device PFET 420.PFET 420 is clocked with an output latch clock signal 422. In aparticularly useful embodiment, output latch clock signal 422 may becreated by a logical OR of first and second evaluation clock signals 414and 416. Other derivations of output latch clock signal 422 have alsobeen contemplated within the scope of the present principles. In apreferred embodiment, first and second evaluation clocks 414 and 416 arenon-overlapping clock signals. When either of first or second evaluationclock signals 414 or 416 are low, during the precharge phase, PFET 420is turned on to precharge dynamic node 418 to a logic high value. Whenfirst evaluation clock signal 414 is high, during the evaluation phase,PFET 420 is turned off and NFET 410 is turned on, allowing dynamic node418 to be selectively discharged to ground according to the Booleancombination of inputs 402 from evaluation tree 404. When secondevaluation clock signal 416 is high, during the evaluation phase, PFET420 is turned off and NFET 412 is turned on, allowing dynamic node 418to be selectively discharged to ground according to the Booleancombination of inputs 406 from evaluation tree 408. In yet anotherembodiment, PFET 420 is sized to be the smallest device capable ofprecharging the dynamic node 418 within the allocated precharge time.

In a preferred embodiment, first evaluation clock signal 414, secondevaluation clock signal 416 and output latch clock signal 422 areconfigured in a double pumping implementation; however, it is noted thatthe present principles are much broader, as other configurations ofclock signals 414, 416 and 422 are also contemplated. Referring for amoment to FIG. 5, and with continued reference to FIG. 4, a timingdiagram 500 is illustratively depicted for first evaluation clock signal414, second evaluation clock signal 416 and output latch clock signal422 and CPU clock 502, in accordance with one embodiment. It can be seenthat output latch clock signal 422 is the logical OR of first evaluationclock signal 414 and second evaluation clock signal 416. Initially, justprior to time T1 504, clock signals 414, 416 and 422 are simultaneouslylow (i.e., precharge phase), allowing precharge device 420 to prechargedynamic node 418. In a first half of a cycle of CPU clock 502, such asbetween times T1 504 and T2 506 (e.g., at rising edge 514), firstevaluation clock signal 414 pulses high 516 and output latch clocksignal 422 pulses high 518 simultaneously, allowing evaluation tree 404to evaluate dynamic node 418 according to inputs 402. An output 440 ofLSDL device 400 is determined in response to dynamic node 418 and clocksignals 414 and 422 then return low to a precharge phase. In a secondhalf of a cycle of CPU clock 502, such as between times T2 506 and T3508 (e.g., at the falling edge 520), second evaluation clock signal 416pulses high 522 and output latch clock signal 422 pulses high 524simultaneously, allowing evaluation tree 408 to evaluate dynamic node418 according to inputs 406. The output 440 is determined in response todynamic node 418 and clock signals 416 and 422 then return low to aprecharge phase. This process continues over times T3 508, T4 510, T5512, etc. Advantageously, by implementing a double-pumpingconfiguration, a logic evaluation operation is performed in each half ofa cycle of CPU clock 302. It can be seen that clock 422 pulses hightwice in a single cycle.

Referring back to FIG. 4, dynamic node 418 is coupled to the commonjunction of the gates of pre-driver devices PFET 424 and NFET 426. PFET424 and NFET 426 form an inverter pair to invert the signal on thedynamic node 418 and provide gain to strengthen the signal. PFET 424 andNFET 426 prevent back-propagation of the signal on node 436 to thedynamic node 418. PFET 424 and NFET 426 are serially coupled to parallelNFETs 428 and 430. Header device NFET 428 is switched by output latchclock signal 422 and prevents the forward propagation of the signal ondynamic node 418 onto the latch during the precharge phase.

Feedback devices NFET 430 and PFET 432 receive feedback from the output440 of the LSDL device 400 to restore the charge to the latched value. Alatch is formed by inverter pair PFET 424 and NFET 426 and feedbackdevices NFET 430 and PFET 432. PFET 432 and NFET 430 allow the value inthe latch to be held as long as the clock signal 422 is kept low. In oneembodiment, LSDL device 400 may include cut feedback device PFET 434,which is clocked by output latch clock signal 422. PFET 434 cuts thefeedback through PFET 432 during the evaluation phase to preventconflict between PFET 432 and NFET 426 when node 436 switches from logichigh to logic low. PFET 434 increases loading on the clock, leading toan increase in clock power consumption, but providing increased speedand circuit robustness. The signal at node 436 drives the output 440 byoutput driver inverter 438 to mitigate noise propagation from dynamicnode 418.

Advantageously, time division multiplexed LSDL device 400 enableshigh-speed double-pumping with a simplified circuit architecture bygenerating a third clock signal (i.e., output latch clock signal 422).First, the three high stacked NFET stack (NFETs 228, 232 and 236 in FIG.2) of LSDL device in NAND form 200 is returned to a two high stack(NFETs 426 and 428 in FIG. 4), which is similar to that of LSDL device100 of FIG. 1. Assuming all devices are sized to be the same, LSDLdevice 400 will drive more current, thereby increasing performance.Second, duplicated devices, such as pre-charge devices (PFETs 210 and218), foot devices (NFETs 212 and 220), PFET pre-driver devices (PFETs226 and 230) and cut feedback devices (PFETs 242 and 244) in LSDL devicein NAND form 200 of FIG. 2 are returned to a single device in LSDLdevice 400 of FIG. 4 by providing an output latch clock signal 422. Thereduction in the number of devices will lead to a further increase inperformance. Third, foot devices (NFETs 212 and 220) in LSDL device inNAND form 200 of FIG. 2 are moved above the evaluation trees (NFETs 410and 412) in LSDL device 400 of FIG. 4. By positioning NFETs 410 and 412above evaluation trees 404 and 408, node diffusion capacitance from thedynamic node 418 to evaluation trees 404 and 408 is reduced and clockedNFETs 410 and 412 are located closer to the output, leading to anincrease in performance. Table 1 summarizes LSDL device in NAND form 200of FIG. 2 as compared with LSDL device 400 of FIG. 4.

TABLE 1 a comparison of the NAND form LSDL device 200 of FIG. 2 with theLSDL device 400 of FIG. 4. LSDL device in NAND LSDL device 400 form 200of FIG. 2 of FIG. 4 Number of 3 (NFETs 228, 232 and 236) 2 (NFETs 426and 428) NFET stacks Clocked NFET Bottom footer location Aboveevaluation trees location Number of 2 (PFETs 210 and 218) 1 (PFET 420)pull-up PFETs

In one illustrative example, the present principles may be applied to atwo read/two write port register file (RF). Implementing the doublepumping scheme, a two read/two write port RF can be translated into aone read/one write port RF with four sets of addresses, which needs atotal of 32 (16 for read and 16 for write) time division multiplexedLSDL partial address decoders, such as, for example, LSDL device 400 ofFIG. 4. The early true/complement addresses may be evaluated by a firstevaluation clock signal 414 and the late true/complement addresses maybe evaluated by the second evaluation clock signal 416. During aprecharge phase, when first evaluation clock signal 414, secondevaluation clock signal 416, and output latch clock signal 422 are low,dynamic node 418 is precharged to a logic high. During an evaluationphase, when first evaluation clock signal 414 and output latch clocksignal 422 are simultaneously high, dynamic node 418 is evaluated tostay at a logic high value or go to a logic low value by evaluation tree404. When second evaluation clock signal 416 and output latch clocksignal 422 are simultaneously high, dynamic node 418 is evaluated tostay at a logic high value or go to a logic low value by evaluation tree408. The dynamic node 418 drives pre-driver devices PFET 424 and NFET426 and node 436 drives the output as a partially decoded line by theoutput driver 438. Returning back to a precharge phase, when firstevaluation clock signal 414, second evaluation clock signal 416 andoutput latch clock signal 422 are low, data is latched by feedbackdevices PFET 432 and NFET 430.

Referring now to FIG. 6, a block/flow diagram showing a system/methodfor enabling double pumping in an LSDL device in NAND form 600 using twoevaluation trees tied to two separate clocks is illustratively depictedin accordance with one illustrative embodiment. In block 602, a firstdynamic node is precharged during a precharge phase of a firstevaluation clock signal. Precharging the first dynamic node may includecontrolling the evaluation of the first dynamic node by, for example,providing a foot device (e.g., NFET) clocked to the first evaluationclock signal and coupled between an output of a first evaluation treeand a ground. In one embodiment, the precharge phase of the firstevaluation clock signal is a low signal. In block 604, the first dynamicnode is evaluated in response to one or more first input signals of thefirst evaluation tree during an evaluation phase of the first evaluationclock signal. The first evaluation tree may receive a plurality ofinputs. The first evaluation tree performs Boolean computations on thefirst input signals during the evaluation phase to provide an output onthe first dynamic node.

In block 606, a second dynamic node is precharged during a prechargephase of a second evaluation clock signal. Precharging the seconddynamic node may include controlling the evaluation of the seconddynamic node by, for example, providing a foot device (e.g., NFET)clocked to a second evaluation clock signal and coupled between anoutput of a second evaluation tree and a ground. In yet anotherembodiment, the precharge phase of the second clock signal is a lowsignal. In block 608, the second dynamic node is evaluated in responseto one or more second input signals of a second evaluation tree duringan evaluation phase of the second evaluation clock signal. The secondevaluation tree may also receive a plurality of inputs. The number ofinputs of the first and second evaluation trees does not necessarilyhave to be equal. The second evaluation tree performs Booleancomputations of the second inputs to provide an output on the seconddynamic node.

In block 610, a signal of the LSDL circuit is outputted in response toat least one of the first dynamic node during the evaluation phase ofthe first evaluation clock signal and the second dynamic node during theevaluation phase of the second evaluation clock signal. In oneembodiment, providing an output of the LSDL circuit includes applying alogical NAND operation in response to the first and second dynamic nodesonto a first output node. It is noted that the present principles arenot limited to a logical NAND operation, but may include any logicaloperation. In yet another embodiment, providing an output of the LSDLcircuit includes preventing forward propagation of the signal on thefirst and second dynamic nodes during the precharge phase of the firstand second evaluation clock signals.

The output of the LSDL circuit may be fed back through first and secondfeedback devices to the first output node, allowing the value in thelatch to be held during the precharge phase of the first and secondevaluation clock signals. In still another embodiment, feeding back theoutput of the LSDL device may include cutting the feedback through thefirst feedback device during the evaluation phase of at least one of thefirst and second evaluation clock signals. The signal on the firstoutput node is driven to the output of the LSDL circuit by an inverterto mitigate noise propagation from the first and second dynamic nodes.The output of the LSDL circuit may be latched during the precharge phaseof the first and second evaluation clock signals.

Referring now to FIG. 7, a block/flow diagram of a system/method forenabling double pumping in an LSDL device with a simplified circuitarchitecture is provided in accordance with one illustrative embodiment.In block 702, a dynamic node is precharged during a precharge phase of afirst evaluation clock signal and a second evaluation clock signal.Precharging the dynamic node may include controlling the evaluation ofthe dynamic node by, for example, providing a first foot device (e.g.,NFET) clocked to a first evaluation clock signal and coupled between anoutput of a first evaluation tree and the dynamic node and providing asecond foot device (e.g., NFET) clocked to a second evaluation clocksignal and coupled between an output of a second evaluation tree and thedynamic node. Further, precharging the dynamic node may include reducingthe diffusion capacitance from the dynamic node to a first and secondevaluation tree. In one embodiment, the precharge phase of the firstevaluation clock signal and the second evaluation clock signal is a lowsignal.

In block 704, the dynamic node is evaluated in response to one or morefirst input signals of the first evaluation tree during an evaluationphase of the first evaluation clock signal. The first evaluation treemay perform Boolean computations on a plurality of inputs to provide anoutput on the dynamic node during an evaluation phase of the firstevaluation clock signal. In one embodiment, the evaluation phase of thefirst evaluation clock signal is a high signal. In block 706, thedynamic node is evaluated in response to one or more second inputsignals of the second evaluation tree during an evaluation phase of thesecond evaluation clock signal. The second evaluation tree may performBoolean computations on a plurality of inputs to provide an output onthe dynamic node during an evaluation phase of the second evaluationclock signal. In one embodiment, the evaluation phase of the secondevaluation clock signal is a high signal. Preferably, the first andsecond evaluation clock signals are non-overlapping.

In block 708, a signal of the LSDL circuit is outputted in response tothe dynamic node according to an output latch clock signal. In aparticularly useful embodiment, the output latch clock signal is createdby a logical OR of the first and second evaluation clock signals. Otherderivations of the output latch clock signal have also been contemplatedwithin the scope of the present principles. Outputting a signal of theLSDL circuit may include inverting the signal from the dynamic node ontoa first output node. In one embodiment, outputting a signal may includepreventing forward propagation of the signal on the dynamic node duringthe precharge phase of the first and second evaluation clock signals.The output of the LSDL circuit may be fed back through a first andsecond feedback device onto the first output node during the prechargephase of the first and second evaluation clock signals. In yet anotherembodiment, the feedback through the first feedback device may be cutduring the evaluation phase of at least one of the first and secondevaluation clock signals. The signal on the first output node may bedriven to the output of the LSDL circuit by an inverter to mitigatenoise propagation from the dynamic node. The output of the LSDL circuitmay be latched during the precharge phase of the first and secondevaluation clock signals.

Having described preferred embodiments of a system and method for timedivision multiplexed limited switch dynamic logic (which are intended tobe illustrative and not limiting), it is noted that modifications andvariations can be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments disclosed which are within the scopeof the invention as outlined by the appended claims. Having thusdescribed aspects of the invention, with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A method for enabling double pumping in a limitedswitch dynamic logic (LSDL) circuit, comprising: precharging a dynamicnode in accordance with a first clock signal and a second clock signal;evaluating the dynamic node to a first value in response to one or morefirst input signals of a first evaluation tree in accordance with thefirst clock signal; evaluating the dynamic node to a second value inresponse to one or more second input signals of a second evaluation treein accordance with the second clock signal; and outputting a signal ofthe LSDL circuit in response to the dynamic node.
 2. The method asrecited in claim 1, wherein precharging includes: reducing diffusioncapacitance from the dynamic node to the first evaluation tree during aprecharge phase of the first clock signal; and reducing diffusioncapacitance from the dynamic node to the second evaluation tree during aprecharge phase of the second clock signal.
 3. The method as recited inclaim 1, wherein outputting the signal of the LSDL circuit includesinverting a signal from the dynamic node onto a first output node. 4.The method as recited in claim 1, wherein precharging includespreventing forward propagation of a signal on the dynamic node during aprecharge phase of the first and second clock signals.
 5. The method asrecited in claim 1, wherein outputting the signal of the LSDL circuitincludes feeding back the signal of the LSDL circuit through first andsecond feedback devices to a first output node.
 6. The method as recitedin claim 5, wherein feeding back the output includes cutting thefeedback through the first feedback device during an evaluation phase ofat least one of the first and second clock signals.
 7. The method asrecited in claim 3, wherein outputting the signal of the LSDL circuitincludes inverting the signal from the first output node to an output ofthe LSDL circuit to mitigate noise propagation from the dynamic node. 8.The method as recited in claim 1, wherein outputting includes outputtingthe signal of the LSDL circuit in response to the dynamic node inaccordance with an output latch clock signal, wherein the output latchclock signal is a logical OR of the first evaluation clock signal andthe second evaluation clock signal.
 9. The method as recited in claim 1,wherein the first clock signal and the second clock signal arenon-overlapping.
 10. The method as recited in claim 1, whereinoutputting the signal of the LSDL circuit includes latching the outputduring a precharge phase of the first and second clock signals.
 11. Themethod as recited in claim 1, wherein a precharge phase of the first andsecond clock signals is a low signal and an evaluation phase of thefirst and second clock signals is a high signal.
 12. A method forenabling double pumping in a limited switch dynamic logic (LSDL)circuit, comprising: precharging a dynamic node in accordance with afirst and second evaluation clock signal, wherein precharging includesreducing diffusion capacitance from the dynamic node to a firstevaluation tree according to the first evaluation clock signal and fromthe dynamic node to a second evaluation tree according to the secondevaluation clock signal; evaluating the dynamic node to a first value inresponse to one or more first input signals of the first evaluation treein accordance with the first evaluation clock signal; evaluating thedynamic node to a second value in response to one or more second inputsignals of the second evaluation tree in accordance with the secondevaluation clock signal; and outputting a signal of the LSDL circuit inresponse to the dynamic node according to an output latch clock signal,wherein the output latch clock signal is a logical OR of the firstevaluation clock signal and the second evaluation clock signal.
 13. Themethod as recited in claim 12, wherein outputting the signal of the LSDLcircuit includes inverting a signal from the dynamic node onto a firstoutput node.
 14. The method as recited in claim 13, wherein outputtingthe signal of the LSDL circuit includes cutting a feedback through afirst feedback device during an evaluation phase of at least one of thefirst and second evaluation clock signals.
 15. A method to enable doublepumping in a limited switch dynamic logic (LSDL) circuit, comprising:precharging a first dynamic node in accordance with a first evaluationclock signal; evaluating the first dynamic node to a first value inresponse to one or more first input signals in accordance with the firstevaluation clock signal; precharging a second dynamic node to a secondvalue in accordance with a second evaluation clock signal; evaluatingthe second dynamic node in response to one or more second input signalsin accordance with the second evaluation clock signal; and outputting asignal of the LSDL circuit in response to at least one of the firstdynamic node in accordance with the first evaluation clock signal andthe second dynamic node in accordance with the second evaluation clocksignal
 16. The method as recited in claim 15, wherein: precharging thefirst dynamic node includes controlling evaluation of the first dynamicnode according to the first evaluation clock signal; and precharging thesecond dynamic node includes controlling evaluation of the seconddynamic node according to the second evaluation clock signal.
 17. Themethod as recited in claim 15, wherein outputting the signal of the LSDLcircuit includes applying a logical NAND operation on at least one ofthe first and second dynamic nodes onto a first output node.
 18. Themethod as recited in claim 17, wherein outputting the signal of the LSDLcircuit includes feeding back the output of the LSDL circuit to firstand second feedback devices.
 19. The method as recited in claim 18,wherein feeding back the output includes: cutting the feedback throughthe first feedback device during an evaluation phase of the firstevaluation clock signal; and cutting the feedback through the firstfeedback device during an evaluation phase of the second evaluationclock signal.
 20. The method as recited in claim 17, wherein outputtingthe signal of the LSDL circuit includes inverting the first output nodeto mitigate noise propagation from the dynamic node.